Photosensitively opacifiable glass



Sept. 8, 1953 s. D. STOOKEY PHOTOSENSITIVELY OPACIFIABLE GLASS Filed July '7, 1950 TRANSPARENT GLASS? DUI-UH 333337 LINEAR OPAC/F/ED GNP/P3 INVENTOR JrA/vz EY 00/YALD Jroolre'r 1! TTORNE K Patented Sept. 8, 1953 PHOTOSENSITIV ELY OPACIF-IABL'E GLASS Stanley Donald Stoo'key, Corning,N 'Y assignor 'to Corning Glass Works, Corning, N. 'Y., a corporation of New York Application'July-l, 1950, Serial No. 172,596

This invention relates to .photosensitively opacifia'cle glasses or glasses which are capable of being thermally opaci'fied following only exposure to short-Wave radiations. 4

Photosensitive glasses of this type, containing gold as the primary photosensitizing agent, are described in my pending application Serial No. 69,769, filed January 7, 1949, now Patent No. 2,515,943 issued July'8, 1950. For successful developrnent, such gold-containing glasses must be held for extended periods of "time at temperatures close to their softening points. Because of their resulting tendency to :soften, these glasses have not been entirely satisfactory for theproduction of all types "o'fware, however, and close temperature control must be employed to prevent undue deformation of such were as can'be readilymade. '(As used-herein,-the softenin point of a glass is that defined inan -article entitled A method for measuring the softening temperature of glass, by J. T. Littleton, Jour. Amer. Ceram.

BBQ-10,259 (19 27 I have now discovered photosensitively opacifiable glass compositions which avoid these difficulties. These glasses employ silver as the primary photosensitizing agent and are particulariyadvantageous'in that they can he satisfactorily developed in considerably shorter times and/or at considerably lower temperatures, whereby softening and resultant deformation of Were can be avoided. Moreover, the present glasses possess 'argreater degree of photosensitivity.

The glasses according to the present invention 75% SiOz, the indicated proportion of at least "one alkali metal oxide selected from the group consisting of up to 2% Li2O, 5% to 18% Nazi),

and up to 13% K20, the selected alkali metal oxide'including Nazi), the'total alkali metal-oxide content being 12% to 18%, 2% "to 12% Alcoa,

'0.0001% to 0.3% of silver computed as AgCl,

0.005% to 0.05% CeO2, 1.8%"130 3.0% Of analytically determined fluorine, and the indicated proportion of a halogen selected from the group consisting of 0.01% to 0.2% of analytically determined chlorine, 0.02% to 0.4% of analytically determined bromine, and0.03% to 0.6% of analytically determined iodine. These essential constituents must amount to at least 85% of the total composition.

The base glass, exclusive of photosensitizing andopeoifying agents, comprises silica, :at least one alkali metal oXicie as indicated, and alumina in the amounts specified. The use of these ingredients in proportions outside the indicated ranges results in an unsatisfactory product. For example, an excess of S102 or .a defiiciency of alkali metal oxideproduces ag lass which is difiicult to melt and which tends to spontaneously opacify during working. On the other hand, an excess of alkali metal oxide or too little S102 objectionably decreases the chemical stability of the glass. At 'l'ea 'st'2% Alz'Os'is necessary to prevent spontaneous opacificati'on but more than 12% objectionably hardens the'zglass.

Preferably, the alkali "metal oxide comprises Na2O alone. L and/or K20 152111 be employed in combination with NazOin the indicated proportions, however. More than the indicated maximum proportionof LiztD -tends to objectionably'softe'n the glass and'toresult in devitrification, while-larger amountsof K20 cause the glass to become to'o"hardand'tendtobring about spontaneous opacification.

Small amounts of B203 may advantageously be employed to facili-tate melting and working of the glass. However, 'a'mountswgreater than 5% tend to Weaken the photosensitivity of the glass and -to-cause it-to be excessively soft.

V The-oxides of'the divalent metals Be, Mg, Ca, 'Zn, Sr, Cd, and Ba may also be'inoluded within the limits specified below in order to generally improve the chemical durability of the present lasses. Because of their tendency to induce spontaneous opacification, however, 'BeO, MgO, and can should not be presentin amounts exceeding "3% either individually or collectively; :Z'n'O, "SrO, land'B'aO in amounts up to 12%, and 'CdO in amounts up to 5%. Of these divalent oxides, ZnO has been found the most desirable. Regardless of which divalent oxides are em- "ployed, "however, the total content thereof shotil d not'ibe greater than 12 It is essential that the'presence of materials which strongly "absorb ultraviolet radiations be avoided. 'Su'ch absorptive constituents include most'glass colorants, particularly selenium or its compounds and oxides of iron, copper, uranium, and vanadium, as'well as the non-coloring oxides Of arsenietnauiumana'lead.

Thesilvormay beintroduced into the batch as any salt or compound thereof. Preferably, a water solution of silver nitrate isemployed. The minimum amountof silver-effective to produce a noticeable degree of photosensitivity is-0.0001% oompultedas-AgGl. The'opacified image is generally white whenthe silver content is less than :about 0.002%. .As theproportionof :silver is increased, however, a yellowish tint tendsto be im- 3 parted to the opaque image, particularly with long or intense irradiation. With a silver content in excess of about 0.05%, the image is almost invariably colored. More than 0.3% of silver tends to spontaneously color the glass throughout during melting or reheating.

The presence of C602 is necessary in order to promote and enhance the photosensitivity of the silver. Less than 0.005% CeOz is relatively inefiective, while more than about 0.05% causes sufficient absorption of ultraviolet radiations to effectively destroy the photosensitivity of the glass. As a source of CeOz, a material known as cerium hydrate, having a cerium content equivalent to about 75% CeOz, has been found satisfactory although other salts and compounds of cerium may be used.

The amount of fluorine incorporated into the glass must be insuificient to cause opacification upon reheating. The fluorine may be introduced into the batch as any of its common compounds, such as sodiumor potassium-silicofluoride, cryolite, or alkali metal fluoride. It is impossible, however, to state a definite amount of fluorine ing in the glass must not be less than 0.01% chlorine, 0.02% bromine or 0.03% iodine and not more than 0.2% chlorine, 0.4% bromine or 0.6% iodine. Smaller amounts than those indicated are ineffective to activate the silver, whereas larger amounts tend to cause spontaneous opacification. These three halogens may be used collectively, if desired. When so employed, however, their total content, computed on a mole equivalent basis, must be Within the limitations set forth above for any one taken individually.

The presence of up to 0.2% of antimony oxide computed as 510203 or up to 0.1% SD02 is advantageous for increasing the photosensitivity of the glass. Greater amounts of either oxide tend to cause overall coloration of the glass when melted, thus destroying the photosensitivity. SbzOs also exerts a desirable fining action during melting of the glass, and its presence is generally preferred to that of SnOz.

The following batches are illustrative of glass compositions falling within the scope of my invention (weight in pounds except the gold solution, which is expressed in cc.):

H): Borax (anhydrous) C3003 Corn Starch which, when introduced into the batches for the present glasses, will produce the desired result under all conditions, because a considerable amount is unavoidably lost by volatilization in the melting of the batch, depending upon the time and temperature of melting and the type of melting container, that is, whether open or closed. I have nevertheless determined that the amount of fluorine remaining in the final glass, that is, analytically determined fluorine, must be not less than about 1.8% or greater than about 3.0% to produce the present result, regardless of the quantity of fluorine added to the batch. Less than about 1.8% fluorine results in little or no opacification, while more than about 3.0% fluorine results in spontaneous opacification.

In what form the fluorine exists in the unopacifled glass is not definitely known, but it is believed that at least some of it is in the form of alkali metal fluoride dissolved in the glass. In any event, it has been determined that the opacifying crystallites in the exposed and developed glass contain fluorine and are composed large- 1y, if not entirely, of alkali metal fluoride, in particular sodium fluoride.

The presence of chlorine, bromine, or iodine in the amounts indicated is necessary to activate the silver and make it efi'ectively photosensitive. Like fluorine, these other halogens tend to volatilize during melting; but I have found that the analytically determined amount remain- The silver nitrate is incorporated in the above batches as a dilute aqueous solution. The gold solution is prepared by dissolving metallic gold in aqua regia in the proportions of 25 grams of gold per cc. of solution.

As is well known, the exact compositions of halogen-containing glasses cannot be calculated with accuracy from their batches. In the first place, as pointed out above, considerable halogen in variable amounts is lost during melting and the exact halogen content of the final glass can be determined only by analysis. Moreover, the halogens are anions, but with which cation or cations they are combined is not definitely known. The calculated final content of the halogens computed as F, Cl, Br, or I respectively is therefore independent of the base composition, which is always computed on the oxide basis.

For practical purposes, however, the calculated percentages of the oxides and the calculated percentages of the halogens are generally computed together to a total of 100%, although this results in a slight error in the expressed amounts of the various constituents as compared to their analytical amounts. The calculated compositions of such glasses are therefore approximate.

The calculated composition of the glass obtained by melting batch l, for example, is 69.4% SiOz, 16.7% NazO, 10.1% A1203, 0.6% B203, 0.0017 of silver computed as AgCl, 0.01% 0e02, 0.09% 310203, 2.9% F, and 0.25% Br. By comparison a glass produced by actuall'y melting"this" batch ina large commercial melting unit at-a top'temperature of approximately 1400 G. con-- tained by analysis 2.6% fluorine-and;0.2% bromine; The composition ofthis glass recalculated is then 69.6% SiOz, 16.8% NazO; 10.1% A1203, 0. 3% B203, :001-7% of silver computed as AgCI, 0.01% C602, 0.09%; 313203; 2.6% F, and

The glass produced by melting batchlpossesses physical propertiespa-rticularly desirable for melting and forming purposesand'comprisesa preferred embodiment of my invention. Due

to the presence of ZnO, the glassmeltedfrom batch 2 possesses goodchemical durability and represents another preferred embodiment. The

composition of this latter glass, computed andrecalc-ulated in the manner described above; is

69.1% S102, 16.5% NazO, 6.6% A1203, i.8% ZnO, 0;002% of silver computed as AgCl, 0.02% 0e02, 0.1 SbzOa; 2.5% Fand 0.2% B1.

It will be noted that all of the-batches contain a mild reducing agent, the presence ofwhich during melting is essential. Wheneither a bromide or an iodide, such as NaBr or NaI', is used to furnish the halogen (other than fluorine), such compound itself functions as the reducing agent. If a chloride such as NaGl is usedto furnish such halogen, then, except in the case of NHiCl, another material such as corn starch, as-

in batch 5, must be-added.

In any event, the addition to the batch of a minor amount of a reducing agent other thantendto render the glass spontaneously op-acifi-- able upon thermal treatment.

An oxidizing agent such as sodium nitrate is desirably employed with the larger proportions of silver, generally above about 0.05%, to insure that the silver dissolves in theglass. If the glassis also to contain gold as in batch 4, the use of an oxidizing agent is necessary.

The present glasses are clear and transparent when melted, worked, and cooled, and will so remain when merely reheated. short-wave radiations, preferably those between 3000 and 3500 Angstroms, produces an invisible, latent image therein. This latent image, present only in the exposed portions of the glass, is-converted to avisible, opaque image by subsequent heating. If a photographic negative or stencil is interposed between. the glass. and. the source of radiation, only selected areas of the glass will be exposed, and the image formed will be a reproduction of the negative or stencil. The exposure time may vary from about ten seconds to an hour or longer, depending on the particu lar glass composition, the image characteristics desired, and the intensity. and type of radiation employed. With a Gil-ampere carbon are at a distance of one foot, an average exposure can be accomplished in about-thirty seconds. Genorally speaking, exposure times of over about 5 to ID minutes are unnecessary.

The latent image produced in the glass during exposure is converted to a visible opaque image by a two-stage. development. The initial step-involves heating the exposed glass for a time and Exposure to.

6. at a temperature varying from about one minute at 50 C. above the. softening point of the. glass to about onehour at about 150 C. below the.

softening point. Temperatures lower than 150 1 C. below the softening point. are ineffective,-v and temperatures higher than 50 C. above the softening point are. both impractical and detrimental to the image. Preferablmunless a shaping operation is-to be carried out simultaneously, the temperature should be about 50 to- C. below the softening point to accomplish this initial' development within a reasonable time and toavoid possible deformation of the article or sticking of the article to its support. Too rapid heating of the glass above 500 C. tends to destroy the latent image before it can be developed; and should be avoided.

This initial heat treatment doesnot cause any.

opacification but is nevertheless essential for the wise transparent. It is believed that duringsuch heat treatment submicroscopic. nuclei of colloidalsilver are formed in the irradiated portions ofthe glass and-that, if the silver content is above about 0.002%, the silver nuclei will be. of a size and number sufficient totend to. cause a yellow ish coloration of the glass.

Following such preliminary heat treatment the glass is cooled to a temperature below about 500 C. During this step, also, no further visiblechange in the glass occurs.

submioroscopic nuclei of the opacifying agent or agents, that is, alkalimetal fluorides, are: formed on the silver nuclei as a result of this cooling,

and that the formation of such invisible fluoride nuclei is entirely dependent upon the presence of the silver nuclei without which opacification of the latent image could not be initiated. While the glasses must be cooled to below this temperature to accomplish the subsequentopacification, how much below seems to be immaterial and they may be cooled to room temperature if desired.

Having been so cooled, the glass is again heated at a temperature and for a time sufiicient to cause the fluoride nuclei to grow and form opacifying crystallites. For this purpose the temperature should be not lower than about 100 C. below the softening point. The reheating time depends on the density desired in the final image and on the temperature, greater densities requiring correspondingly longer times and higher temperatures shorter times. For average image development, a period of 3 to 15 minutes is usually adequate. The finished glass is thereafter cooled to room temperature.

It is only during this second heating that the final opacified image is developed and then only in the irradiated portions of the glass. Such image will appear white or uncolored unless the preliminary heating has caused development of a yellowish tint as described above. The opacity will be more or less dense according to the nature of the exposure and the initial heat treatment, which determine the number of nuclei formed, and also the final heat treatment, which determines the size to which the opacifying crystallites grow.

With some glasses containing fluorine in the upper half or so of the indicated range, it may be found" that the initial heat treatment and It is believed that.

intermediate cooling may be omitted and that the desired opaque image can be obtained with a single heat treatment. In general, however, it will be found that the described two-step heat treatment is necessary.

Various effects can be achieved with the present glasses. For example, difierent shades or hues can be produced in the same article by exposing different areas to different intensities of irradiation or for difierent times. Again, the temperature employed in either heating step or the duration thereof has an effect on the shade and/r hue produced. The use of progressively slighter exposures together with progressively longer or higher-temperature heating in the first heating step, while keeping the temperature below 550 C. in the final heating step, results in the production of yellow, brown, orange, rose, purple, blue, and green hues in this order.

A further variation is obtained by the inclusion of SbzOa and SnOz, which together impart agrayish or a pinkish tint to the opal image depending on the proportions in which they are used. The total of SbzOa and SnOz combined should not exceed 0.2%, and the maximum amount of SnOz should not exceed 0.1%. A pinkish coloration can also be produced by the inclusion of up to 0.01% of gold computed as Au. A colored background can be provided by including a suitable coloring material such as cobalt oxide or manganese oxide in the glass.

Further exposure of irradiated areas between the two heat-treating steps surprisingly effects a reversal of the opal development, that is, the re-exposed areas remain clear and transparent following the second heat treatment. For example, an overall initial exposure of an article followed by heating and subsequent re-exposure of a portion thereof thus produces a transparent image against an opaque background.

Surface opacity can be produced by special treatment in glasses of the present type melted from batches containing no silver. By applying to the surface of such a glass a finely divided material containing silver or a compound of silver and heating the glass and the material while in contact in accordance with conventional silver-staining procedure, an exchange of silver for alkali metal in the glass is eiiected. The surface of such a silver-stained glass, when subsequently held at a temperature above about 550 C. for about 15 minutes or longer and then cooled below about 500 0., becomes opacified upon reheating to a temperature not lower than about 100 C. below the softening point of the glass. Alternatively, the glass and the silver-staining material can be heated to a temperature above about 550 C. for at least 15 minutes, and the silver-stained glass then cooled and reheated as indicated. No exposure to short-wave radiations is necessary to produce such opacity. Reversal of this opal formation can be effected by exposure of the stained area in the usual manner prior to the final heat treatment. Such method of producing surface opacity in glass is claimed in my pending application S. N. 288,313, filed May 16, 1952, which is a division of this application.

The inclusion of corn starch in the batch in amounts greater than that permissible for normal development procedures but not over about 0.6% on the basis or the glass, or of another reducing agent in an amount to provide the equivalent reducing power, produces a surprising effect in that the tendency to spontaneous opacification upon heating is thereby reversed by exposure of the glass to short-wave radiations prior to such heat treatment. Exposure of such a glass in selected areas followed by heating then renders the glass opaque in unexposed areas, but clear and transparent in exposed areas. The thermal conditions for opal development in these glasses are identical with those of the final heat treatment of the developing process described above.

The glasses of this invention and articles made therefrom containing opacified images are useful and desirable for many purposes, both ornamental and utilitarian. Of particular use and desirability are glass sheets in which the image consists of a series of narrow, opacified, linear strips or portions extending through the sheet from one face to the other at any suitable angle to the plane thereof, as shown, only by way of example, in the accompanying drawing, in which:

Fig. 1 is a plan view of a transparent glass sheet having linear opacified strips in accordance with my invention, the thickness of the sheet and the opacified portions being exaggerated for convenience, and

Fig. 2 is a sectional view on line 2-2 of Fig. 1. The spaces between the opacified strips are clear and transparent, and are of such width as to render the opacified strips effective as louvers whereby light can be transmitted in a direction perpendicular to the face of the sheet, but is partially or completely intercepted in a direction at an angle to the face of the sheet and to the strips.

The present glasses are also extremely useful in producing such completely opalized articles as tableware or incandescent lamp bulbs. Because of the variety of effects obtainable with the present glasses, simultaneous production of alltransparent, all-opal and partially opalized ware from a single glass melt is possible.

When the present glasses are to be used in the manufacture of tempered opalware the article can be inspected, prior to opacification and tempering, for stones and other imperfections which would normally cause breakage. A partially opacified article may also be tempered without setting up undue strains between the opacified and transparent portions thereof. Thus for the first time a tempered article having both transparent and opaque areas can be produced. As is well known, prior articles partially opacified by gradient heating become completely opacified When heated for tempering.

Photosensitive glasses containing from 0.05% to 0.3% of silver computed as AgCl are described and claimed in pending application Serial No. 513,441, filed December 8, 1943, by William H. Armistead, now Patent 2,515,936, issued July 18, 1950. Such glasses, when exposed and subsequently heated, develops a transparent yellow coloration in the exposed portions, while the unexposed portions remain clear and colorless.

In my pending application Serial No. 513,445, also filed December 8, 1943, now Patent 2,515,939, issued July 18, 1950, I have disclosed and claimed photosensitive glasses similar to those of Armistead but additionally containing sufficient fluorine to render them thermally opacifiable.

My pending application Serial No. 695,801, filed September 9, 1946, now Patent 2,515,940, issued July 18, 1950, describes and claims photosensitively opacifiable glasses containing 0.025% to 0.3% of silver computed as AgCl and 10% to 25% L120, the amount of Li2O being sufiicient to form lithium disilicate crystallites upon exposure and .subsequentheating.

In my pending application Serial No. 1,492,

Ifiled'January 9, 1948, now Patent 2,515,275, is-

sued July 18, 1950, there are described and claimed photosensitive glasses similar to those of Armistead but containing up to 0.1 S0203. Such glasses may also contain sufiicient fluorine to be thermally opacifiable.

I claim:

1. A clear, transparent photosensitive glass comprising essentially 55% to 75% Si02, the indicated proportion of at least one alkali metal oxide selected from the group consisting of up toi2% Li20, to 18% I a2O, and up to 13% K20, the selected alkali metal oxid including Na20, the total alkali metal oxide content being 12% to 18%, 2% to 12% A1203, 0.0001% to 0.3% of silver computed as AgCl, 0.005% to 0.5% 0e02, 1.8% to 3.0% of analytically determinedfluorine, and the indicated proportion of a halogen selected from thegroup consisting of 0.01% to 0.2%

of analytically determined chlorine, 0.02 to 0.4% of analytically determined bromine, and 0.03%

to 0.6% of analytically determined iodine, the essential constituents totaling at least 85%, said glass being thermally opacifiable only in such areas as have been previously exposed to shortwave radiations.

2. The photosensitive glass as claimed in claim 1, which includes up to 0.2% antimony oxide computed as SbzOs.

3. A clear, transparent photosensitive glass comprising essentially 55% to 75% S102, 1.2% to 18% M120, 2% to 12% A1202, 0.0001% to 0.3% of silver computed as AgCl, 0.005% to 0.05% 0e02, 18% to 3.0% of analytically determined fluorine, and the indicated proportion of a halogen selected from the group consisting of 0.01% to 0.2% of analytically determined chlorine, 0.02% to 0.4% of analytically determined bromine, and 0.03% to 0.6% of analytically determined iodine, the essential constituents totaling at least 85%, said glass being thermally opacifiable only in such areas as have been previously exposed to short-wave radiations.

4. A. clear, transparent photosensitive, glass comprising essentially 55% to 75% $002, 12% to 18% NagO, 2% to 12% A1202, 0.0001% to 0.3% of silver computed as AqCl. 0.005% to 0.05% 0e02, 1.8% to 3.0% of analytically determined fluorine, and 0.01% to 0.2% of analytically determined chlorine, the essential constituents totaling at least 85%, said glass being thermally opacifiable only in such areas as have been previously exposed to short-Wave radiations.

5. A clear, transparent photosensitive glass comprising essentially 55% to 75% S032, 12% to 18% NazO, 2% to 12% A1202, 0.0001% to 0.3% of silver computed as AgCl, 0.005% to 0.05% 0e02, 1.8% to 3.0% of analytically determined fluorine, and 0.02% to 0.4% of analytically determined bromine, the essential constituents totaling at least 85%, said glass being thermally opacifiable only in such areas as have been previously exposed to short-wave r-..diations.

5. A clear, transparent photosensitive glass comprising essentially 55% to 75% Si02, 12% to 18% :NacO, 2% to 12% [ll-20a, 0;000l% to 0.3%

of silver computed as AgCl, 0.005 to 0.05% 0e02, 1.8% to 3.0% of analytically determined fluorine, and 0.03% to 0.6% of analyticallydetermined iodine, the essential constituents totaling at least -85:%, said glass being thermally opaoifiable only in such areas as have been previously exposed to short-wave radiations.

7. The photosensitive glass as claimed in claim 1, which includes up to 5% B203.

8. The photosensitive glass as claimed in claim 7, which includes up to 0. antimony oxide computed as 813203.

9. The photosensitive glass as claimed in claim 1, which includes the indicated proportion of at least one divalent metal oxide selected from the group consisting of up to 3% BeO, up to 3% MgO, 'upto 3% CaO, up to 3% of a mixture of a plurality of such three oxides, up to 12% ZnO, up to 12% SrO, up to 'CdO, and up to 1 the'total divalent metal oxide content being not over 12%.

"1.0. The photosensitive glass as claimed in cl- 9, which includes up to 0.2% antimony computed as $10203.

11. The photosensitive glass as claimed in claim 1, which includes up to 5% E203 and up to 12% 2110.

12. A photosensitive glass as claimed in claim 1, which includes up to 0.1% Sn02.

13. The photosensitive glass as claimed in claim 1, which includes up to 0.2% Sb202 and SnOz combined, the content of Sn02 being not over 0.1%.

14..'The photosensitive glass as claimed in claim 1, Which includes'up'to 0.01% of gold computed as Au.

.15. A clear, transparent photosensitive glass which consists approximately of 69.6% Si02, 16.8% Na20, 10.1%. A1203, 0.6% B203, 0.0017% of silver computed as AgCl, 0.01% 0e02, 0.09% SbzOs, 2.6% of analytically determined fluorine and 0.2% :01" analytically determined bromine, said glass being thermally opacifiable only in such areas as have been previously exposed to short-wave radiations.

.16. A clear, transparent photosensitive glass which consists approximately of 69.1% Si02, 16.5% Na20, 6.6% A1202, 4.8% ZnO, 0.002% of silver computed asAg'Cl, 0.02% 0e02, 0.1% 813203, 2.6% of analytically determined fluorine and 0.2% of analytically determined bromine, said glass being thermally opacifiable only in such areas as have been previously exposed to short- Wave radiations.

17. An article comprising a glass body comtive glass comprising essentially 55% to Si02,' the indicated proportion of at least one alkali metal oxide selected from the group consisting of up to 2% Li20, 5% to 18% Na20, and up to 13% K20, the selected alkali metal oxide including Na20,the total alkalimetal oxide content being 12% to 18%, 2% to 12% A1203, 0.0001% to 0.3% of silver computed as AgCl, 0.005% to 0.05% 0e02, 1.8% to 3.0% of analytically determined fluorine, and the indicated proportion of a halogen selected from the group consisting of 0. 01% to 0.2% of analytically determined chlorine, 0.02% to 0.4% of analytically determined bromine and. 003% to 0.6% of analytically determined iodine, the essential constituents totaling .t least 05%., said glass body containing within its mass .a latent image capable-of being developed, by uniform heating of the entire glass body, into a visible, opaque image.

18. An articlecomprising a glass body composed throughout of a photosensitive glass comprising essentially 55% to 75% Si02, the indicated proto 18% NazO, and up to 13% K20, the selected alkali metal oxide including NazO, the total alkali metal oxide content being 12% to 18%, to 12% A1203, 0.0001% to 0.3% of silver computed as AgCl, 0.005% to 0.05% CeOz, 1.8% to 3.0% of analytically determined fluorine, and the indicated proportion of a halogen selected from the group consisting of 0.01% to 0.2% of analytically determined chlorine, 0.02% to 0.4% of analytically determined bromine, and 0.03% to 0.6% of analytically determined iodine, the essential constituents totaling at least 85%, at least a portion of the glass body containing light-diffusing, fluorine-containing crystallites rendering the same opaque.

19. An article comprising a glass body composed throughout of a photosensitive glass comprising essentially 55% to 75% SiOz, 12% to 18% 1121.20, 2% to 12% A1203, 0.0001% to 0.3% of silvcr computed as AgCl, 0.005% to 0.05% CeOz, 1.8% to 3.0% of analytically determined fluorine, and the indicated proportion of a halogen selected from the group consisting of 0.01% to 0.2% of analytically determined chlorine, 0.02% to 0.4% of analytically determined bromine, and 0.03% to 0.6% of analytically determined iodine, the essential constituents totaling at least 85%, at least a portion of the glass body containing light-diffusing, fluorine-containing crystallites rendering the same opaque.

20. The article as claimed in claim 18, in which the glass includes up to 0.2% antimony oxide computed as $0203.

21. The article as claimed in claim 18, in which the glass includes up to B203.

22. The article as claimed in claim 21, in which the glass includes up to 0.2% antimony oxide computed as SbzOa.

23. The article as claimed in claim 18, in which the glass includes the indicated proportion of at least one divalent metal oxide selected from the group consisting of up to 3% Eco, up to 3% MgO, up to 3% CaO, up to 3% of a mixture of a plurality of such three oxides, up to 12% ZnO, up to 12% SrO, up to 5% CdO, and up to 12% BaO, the total divalent metal oxide content being not over 12%.

24. The article as claimed in claim 23, in which the glass includes up to 0.2% antimony oxide computed as $102.03.

25. The article as claimed in claim 18, in which the glass includes up to 5% E203 and up to 12% ZnO.

26. The article as claimed in claim 18, in which the glass includes up to 0.1% SnOz.

27. The article as claimed in claim 18, in which the glass includes up to 0.2% 310203 and S1102 combined, the content of SnOz being not over 0.1%.

28. The article as claimed in claim 18, in which the glass includes up to 0.01% of gold computed as Au.

29. An article according to claim 18, in which the opaque portion of the glass body forms a predetermined design or image and the remainder is transparent.

30. An article according to claim 18, characterized in that the glass body is tempered.

31. An article according to claim 18, in the form of a glass sheet, selected linear portions of which are opaque and the remainder transparent.

' 32. A glass article according to claim 31, in which the selected linear portions extend from one face of the sheet to the other face,

33. The method of producing a clear, transparent photosensitive glass capable of being thermally opacified only in such areas as have been previously exposed to short-wave radiations, which comprises melting in a batch for a clear, transparent glass comprising essentially 55% to SiOz, the indicated proportion of at least one alkali metal oxide selected from the group consisting of up to 2% H20, 5% to 18% NazO, and up to 13% K20, the selected alkali metal oxide including NazO, the total alkali metal oxide content being 12% to 18%, 2% to 12% A1203, 0.0001% to 0.3% of silver computed as AgCl, 0.005% to 0.05% 0e02, 1.8% to 3.0% of analytically determined fluorine, and the indicated proportion of a halogen selected from the group consisting of 0.01% to 0.2% of analytically determined chlorine, 0.02% to 0.4% of analytically determined bromine and 0.03% to 0.6 of analytically determined iodine, the essential constituents totaling at least said batch containing as a reducing agent up to 0.2% of corn starch on the basis of the glass.

34. The method of making a glass article having an opaque design formed within its mass, which includes the steps of exposing to shortwave radiations at least a portion of an article formed from a clear, transparent glass capable of being thermally opacified only in such areas as have been previously exposed to shcrt-wave radiations and comprising essentially 55% to 75% 8102, the indicated proportion of at least one alkali metal oxide selected from the group consisting of up to 2% L120, 5% to 18% NazO, and up to 13% K20, the selected alkali metal oxide including NazO, the total alkali metal oxide content being 12% to 18%, 2% to 12% A1203, 0.0001% to 0.3% of silver computed as AgCl, 0.005% to 0.05% CeOz, 1.8% to 3.0% of analytically determined fluorine, and the indicated proportion of a halogen selected from the group consisting of 0.01% to 0.2% of analytically determined chlorine, 0.02% to 0.4% of analytically determined bromine and 0.03% to 0.6% of analytically determined iodine, the essential constituents totaling at least 85%, heating the exposed article for a time and at a temperature varying from about one minute at about 50 C. above the softening point of the glass to about one hour at about 150 0. below the softening point of the glass, cooling the article below about 500 0., reheating the article to a temperature not lower than about C. below the softening point of the glass until its exposed portion develops the desired degree of opacity, and then cooling the article to room temperature.

35. The method as claimed in claim 34, in which the glass includes up to 5% B203.

36. The method as claimed in claim 34, in which the glass includes the indicated proportion of at least one divalent metal oxide selected from the group consisting of up to 3% Eco, up to 3% MgO, up to 3% CaO, up to 3% of a mixture of a plurality of such three oxides, up to 12% ZnO, up to 12% SrO, up to 5% C010, and up to 12% BaO, the total divalent metal oxide content being not over 12%.

3'7. The method of producing a glass article containing a clear design against an opaque background, which comprises melting a batch for a clear, transparent glass comprising essentially 55% to 75% SiOz, the indicated proportion of at least one alkali metal oxide selected from the group consisting of up to 2% L120, 5% to 18% NazO, and up to 13% K20, the selected alkali metal oxide including NazO, the total alkali metal oxide content being 12% to 18%, 2% to 12% A1203, 0.0001% to 0.3% of silver computed as AgCl, 0.005% to 0.05% CeOz, 1.8% to 3.0% of analytically determined fluorine, and the indicated proportion of a halogen selected from the group consisting of 0.01% to 0.2% of analytically determined chlorine, 0.02% to 0.4% of analytically determined bromine and 0.03% to 0.6% of analytically determined iodine, the essential constituents totaling at least 85%, said batch containing as a reducing agent 0.2% to 0.6% of corn starch on the basis of the glass, forming the glass into an article, exposing a portion of the article to short-wave radiations and heating the article to a temperature not less than 100 C. below the softening point of the glass.

38. The method as claimed in claim 34, in which a portion of the glass initially exposed to short-wave radiations is re-exposed to such radiations following the initial heating step but prior to the final heating step, such re-exposed portion thereby remaining clear and transparent following the final heating.

39. The method of producing a clear, transparent photosensitive glass, which comprises melting a batch for a clear, transparent glass comprising essentially to Si02, the indicated proportion of at least one alkali metal oxide seleoted from the group consisting of up to 2% L120, 5% to 18% NazO, and up to 13% K20, the selected alkali metal oxide including NazO, the total alkali metal oxide content being 12% to 18%, 2% to 12% A1203, 0.0001% to 0.3% of silver computed to AgCl, 0.005% to 0.5% 0e02, 1.8% to 3.0% of analytically determined fluorine, and the indicated proportion of a halogen selected from the group consisting of 0.01% to 0.2% of analytically determined chlorine, 0.02% to 0.4% of analytically determined bromine and 0.03% to 0.6% of analytically determined iodine, the essential constituents totaling at least said batch containing a. minor amount of an organictype reducing agent.

STANLEY DONALD STOOKE'Y.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,233,622 Lytle Mar. 4, 1941 2,281,076 Nash Apr. 28, 1942 2,314,804 Willson Mar. 23, 1943 2,326,012 Dalton Aug. 3, 1943 2,515,943 Stookey July 18, 1950 FOREIGN PATENTS Number Country Date 110,925 Australia July 11, 1940 

1. A CLEAR, TRANSPARENT PHOTOSENSITIVE GLASS COMPRISING ESSENTIALLY 55% TO 75% SIO2, THE INDICATED PROPORTION OF AT LEAST ONE ALKALI METAL OXIDE SELECTED FROM THE GROUP CONSISTING OF UP TO 2% LI20, 5% TO 18% NAZ0, AND UP TO 13% K20, THE SELECTED ALKALI METAL OXIDE INCLUDING NA2O THE TOTAL ALKALI METAL OXIDE CONTENT BEING 12% TO 18%, 2% TO 12% AL203, 0.0001% TO 0.3% OF SILVER COMPUTED AS AGCL, 0.005% TO 0.5% CE02, 1.8% TO 3.0% OF ANALYTICALLY DETERMINED FLUORINE, AND THE INDICATED PROPORTION OF A HALOGEN SELECTED FROM THE GROUP CONSISTING OF 0.01% TO 0.2% OF ANALYTICALLY DETERMINED CHLORIDE 0.02 TO 0.4 % OF ANALYTICALLY DETERMINED BROMINE, AND 0.03% TO 0.6% OF ANALYTICALLY DETERMINED BROMINE, IODINE, THE ESSENTIAL CONSTITUENTS TOTALING AT LEAST 85%, SAID GLASS BEING THERMALLY OPACIFIABLE ONLY IN SUCH AREAS AS HAVE BEEN PREVIOUSLY EXPOSED TO SHORTWAVE-RADIATIONS.
 34. THE METHOD OF MAKING A GLASS ARTICLE HAVING AN OPAQUE DESIGN FORMED WITHIN ITS MASS, WHICH INCLUDES THE STEPS OF EXPOSING TO SHORTWAVE RADIATIONS AT LEAST A PORTION OF AN ARTICLE FORMED FROM A CLEAR, TRANSPARENT GLASS CAPABLE OF BEING THERMALLY OPACIFIED ONLY IN SUCH AREAS AS HAVE BEEN PREVIOUSLY EXPOSED TO SHORT-WAVE RADIATIONS AND COMPRISING ESSENTIALLY 55% TO 75% SI02, THE INDICATED PROPORTION OF AT LEAST ONE ALKALI METAL OXIDE SELECTED FROM THE GROUP CONSISTING OF UP TO 2% LI20, 5% TO 18% NA20, AND UP TO 13% K20, THE SELECTED ALKALI METAL OXIDE INCLUDING NA20, THE TOTAL ALKALI METAL CONTENT BEING 12% TO 18%, 2% TO 12% AL203, 0.0001% TO 0.3% OF SILVER COMPUTED AS AGCL 0.005% TO 0.05% CE02, 1.8% TO 3.0% OF ANALYTICALLY DETERMINED FLUORINE, AND THE INDICATED PROPORTION OF A HALOGEN SELECTED FROM THE GROUP CONSISTING OF 0.01% TO 0.2% OF ANALYTICALLY DETERMINED CHLORINE, 0.02% TO 0.4% OF ANALYTICALLY DETERMINED BROMINE AND 0.03% TO 0.6% OF ANALYTICALLY DETERMINED IODINE, THE ESSENTIAL CONSTITUENTS TOTALING AT LEAST 85%, HEATING THE EXPOSED ARTICLE FOR A TIME AND AT A TEMPERATURE VARYING FROM ABOUT ONE MINUTE AT ABOUT 50* C. ABOVE THE SOFTENING POINT OF THE GLASS TO ABOUT ONE HOUR AT ABOUT 150* C. BELOW THE SOFTENING POINT OF THE GLASS, COOLING THE ARTICLE BELOW ABOUT 500* C., REHEATING THE ARTICLE TO A TEMPERATURE NOT LOWER THAN ABOUT 100* C. BELOW THE SOFTENING POINT OF THE GLASS UNTIL ITS EXPOSED PORTION DEVELOPS THE DESIRED DEGREE OF OPACITY, AND THEN COOLING THE ARTICLE TO ROOM TEMPERATURE. 